Prova tu stesso - W3.CSS theme

<!DOCTYPE html>
<html>
<title>W3.CSS</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="/lib/w3.css">
<link rel="stylesheet" href="../lib/w3-theme-green.css">
<body>

<div class="w3-card-4">
<div class="w3-container w3-theme w3-card-2">
  <h1>Green</h1>
</div>

<div class="w3-container w3-text-theme"><h2>w3-text-theme</h2></div>

<ul class="w3-ul w3-border-top">
  <li class="w3-theme-l5" style="position:relative">
  <a class="w3-btn-floating-large w3-theme-action w3-right" style="position:absolute;top:-28px;right:16px;">+</a>
  <p>w3-theme-l5 (w3-theme-light)</p>
  </li>
  <li class="w3-theme-l4">
    <p>w3-theme-l4</p>
  </li>
  <li class="w3-theme-l3">
    <p>w3-theme-l3</p>
  </li>
  <li class="w3-theme-l2">
    <p>w3-theme-l2</p>
  </li>
  <li class="w3-theme-l1">
    <p>w3-theme-l1</p>
  </li>
  <li class="w3-theme">
    <p>w3-theme</p>
  </li>
  <li class="w3-theme-d1">
    <p>w3-theme-d1</p>
  </li>
  <li class="w3-theme-d2">
    <p>w3-theme-d2</p>
  </li>
  <li class="w3-theme-d3">
    <p>w3-theme-d3</p>
  </li>
  <li class="w3-theme-d4">
    <p>w3-theme-d4</p>
  </li>
  <li class="w3-theme-d5">
    <p>w3-theme-d5 (w3-theme-dark)</p>
  </li>
</ul>
</div>

</body>
</html>